Divagation is the basis of all knowledge and all conversation. How else can we know things without losing ourselves in the subject, and wouldn’t it be horrible to merely exchange precise, to-the-point, packets of information. Divagation is a sort of linguistic foreplay that never quite comes to grips with information, but is pleasurable in itself. Divagation is what Odysseus did for 10 years before finding his way back to Penelope. Divagation is what Para Handy, captain of the Vital Spark, does best, in the stories by Neil Munro.

And divagation is what I’m doing now. This is the voluntary kind, because I enjoy it. Then there’s this sort.

Faced with Jeremy Paxman, the BBC’s pit bull interviewer, zeroing in on the very question he did not want to answer, the Prime Minister indulged in such a determined and dazzling display of divagation that finally Paxman’s head exploded.

I am indebted to the Daily Mail for this blog post. Bugger. Never thought I’d write that sentence. The fact remains that I’d probably never have heard of this project if the Daily Mail hadn’t chosen to vent their spleen on Patrick Boyle, Earl of Glasgow, who decided to give a team of Brazilian graffiti artists, Os Gemeos, free rein on the oldest part of Kelburn Castle. That was in 2007. Here’s what the BBC News has to say, for a less sensational and prejudiced approach.

There was an agreed 3 year lifespan for the graffiti, pending replacement of the concrete facing on which it was painted, but Lord Glasgow has now petitioned Historic Scotland to keep the graffiti. They have a say in its fate, because Kelburn Castle is a Grade A Listed Building.

I’ve no doubt that a big part of the reason for wanting to keep the graffiti is financial – it brings in visitors. Beyond that, it’s a brilliant piece of public art and should be preserved. I’d love to go and see it. How it can be preserved is another matter. There’s a structural need to replace the concrete facing, in order to avoid further damage to the 13th century masonry. All art – all life – is temporary, and that’s what makes it so precious.

Even so, I want this mural to stick around for as long as possible. It shows the innovative spirit of Scotland that drew me to this place. We’re not a theme park with kilts, whisky, haggis, shortbread, and bagpipes, however well that might sell to the tourists. There’s also the deep-fried Mars bar.

This time lapse video shows the work under construction, from start to finish.

As a prologue to the second half of Series 6, here’s a Guardian blog that recaps what’s happened so far, and the unanswered questions from the first half.

What do you do when you can’t get the Doctor on the phone? Send him a crop circle, one weird enough to make the front page of the Leadworth Chronicle, created by Mini rather than with ropes and boards. Splendid opening scene to Let’s Kill Hitler, trumped by Mels’ arrival in a stolen red sports car, drawing a line through Amy and Rory’s Doctor design. Say who? Mels? Oh, Amy and Rory’s best childhood mate, to whom Amy’s told everything she knows about the Doctor.

She’s a bad girl is Mels, as demonstrated by flashbacks from their childhood, which also show that Rory has never loved anyone but Amy since he was in short trousers. I think we knew that already. Nice reference to Back to the Future when Mels (in Marty McFly mode) has to get Amy to realise that Rory is head over heels in love with her. “The penny’s in the air…the penny drops.”

When the police pursue Mels, the obvious thing is to escape in the Tardis. Where? “You’ve got a time machine. I’ve got a gun. What the hell. Let’s kill Hitler.” I suspect that Steven Moffat came up with the title first, and built the story round that catchy hook, with Hitler as a convenient plot device to further the real business of the episode.

Which is of course to find Melody, Amy and Rory’s baby, who later becomes River Song. As a result of Mels shooting the Tardis – I still haven’t worked out why – they crash land in Hitler’s Chancellery office in 1938. Just in time to knock out the Justice Department robot time ship disguised as a Nazi, which is there to intervene at the end of Hitler’s timeline and give him hell. Cock-up on the scheduling front, because they’re 7 years too early. The ship’s control room bears a striking resemblance to that of the Enterprise in Star Trek, and they’re all miniaturized like the crew in Fantastic Voyage. They’ve even got robot antibodies, looking like metal jellyfish, to destroy unauthorized personnel.

Hitler’s grateful to the Doctor. “Thank you, whoever you are. I think you have just saved my life.” “Believe me, it was an accident.” When the robot revives, Hitler shoots at it, misses, and hits Mels instead, so Rory puts him where he can’t do any more damage. “Right. Putting Hitler in the cupboard.” And there, for all practical purposes, is the end of Hitler in the storyline.

But Mels is part Timelord, having absorbed the energies from the Tardis when she was conceived. As we saw when she broke out of her spacesuit in The Impossible Astronaut, and later regenerated as child in New York at the end of The Day of the Moon. So now she regenerates again, this time as the bodacious River Song, who I am so glad to see again. River as a teenager is even more outrageous than her older self – I keep playing that bit over and over again.

But before regenerating, she reveals herself as Rory and Amy’s daughter. And she also reveals her fascination with the Doctor. “When I was little I was going to marry you.” Unfortunately, the Justice Department ship/Nazi robot recognizes her as the woman who killed the Doctor on 22 April, 2011 at 5:02 pm in Utah.

Still thinking of herself as Mels, and still brainwashed, she kills him with a poisoned kiss. “Am I yours, sweetie?” “Only River Song gets to call me that.” And then she jumps out of the window to enjoy the Third Reich. Amy and Rory follow her on a clothes shopping trip, which involves holding up a restaurant full of people and telling them to take their clothes off.

The Doctor, meanwhile, is dying and unable to regenerate. He calls up the voice interface in the Tardis, rejecting holograms of himself (doesn’t like himself), followed by Rose, Martha, and Donna (“there must be someone left in the universe I haven’t screwed up yet”), before settling on the young Amelia Pond. He finally gets the response – “fish fingers and custard” – that allows him to use the remaining 31 minutes of his life.

Amy and Rory have been zapped by the miniaturization ray wielded by a robot Amy, and find themselves at the mercy of antibodies in the time ship. “OK. I’m trapped inside the giant robot replica of my wife. I’m really trying not to see this as a metaphor.” Brilliant writing. Rescued by the crew, using bracelets that tell the antibodies you’re not food, they watch as robot Amy confronts Mels in the restaurant. “You killed the Doctor on the orders of the movement known as The Silence and Academy of Question.”

Then the Doctor shows up – in top hat and tails. “Doctor, you’re dying and you stopped to change.” He is allowed to question robot Amy. The Silence aren’t a species, but a religious order or movement, who believe that silence will fall when the first and oldest question in the universe is asked. The question itself is unknown. Just as well, really. Reminds me of Arthur C. Clarke’s story, The Nine Billion Names of God.

With the Doctor almost dead, the time ship fulfills its function of punishing criminals who don’t get caught in their lifetimes, by “giving them hell.” Mels burns. But Amy comes to the rescue, using the sonic screwdriver to disable all the protective bracelets so the crew have to beam out of the ship, leaving her and Rory as supper for the antibodies. Mels is now free to go into the Tardis, which teaches her how to fly it, so she can get Rory and Amy out of the time ship. “The Doctor says I am a child of the Tardis. What does that mean?”

The Doctor’s still dying, though, and he has a last message for Mels. “Find River Song and tell her something from me.” We don’t hear his actual words, but it’s pretty obvious that he’s telling Mels, through this message to River, that he loves her. Mels replies, “Well, I’m sure she knows.” But of course she doesn’t, until real Amy instructs robot Amy to show her River Song.

Now Mels knows she’s River Song.

“Is he worth it?” she asks. “Yes, yes he is,” says Amy, and River breathes all her Timelord energy into the Doctor to save his life with one kiss. “Hello sweetie.” Lovely moment.

The Doctor, Amy, and Rory leave her in the tender care of the Sisters of the Infinite Schism to recover, and to live her life without foreknowledge. River has used up all her regenerations. “She will be amazing,” the Doctor says, as he leaves her the blue diary she always carries, tied up in a red ribbon, still unwritten.

River enrolls at Luna University in 5123 to study Archaeology. The professor asks why that subject. “I’m looking for a good man,” she says, with the diary in her hand.

I loved the Doctors verdict on their first meeting, in which River first killed him then saved his life. “As first dates go, I’d say that was mixed signals.”

So we know what happened to Melody. But if she doesn’t kill the Doctor, then what is she in prison for? He won’t tell. And he knows about his forthcoming death in 2011 because he’s seen the Justice Department record on the Tardis console. But Amy and Rory don’t know that he knows.

Then there’s the Silence and that terrible first question in the universe. A great start to the second half of Series 6.